This invention relates to a process for the production of aluminum sulfate and, more particularly relates to a non-evaporative process for the production of drier aluminum sulfate.
In the prior art, a pure aluminum sulfate product has been prepared by digesting pure aluminum trihydrate, a product of the Bayer process, with sulfuric acid. Although the resultant aluminum sulfate product is free from impurities, e.g., iron, the cost of the pure aluminum trihydrate starting material renders the process uneconomical from a practical commercial standpoint.
In U.S. Pat. No. 3,226,188, a process for the production of aluminum sulfate melt having 14 to 20% by weight Al.sub.2 O.sub.3 by reaction under pressure of aluminum hydroxide and sulfuric acid is disclosed.
Aluminum sulfate has also been prepared by reaction of an alumina-bearing ore, e.g., bauxite or clay with sulfuric acid at an elevated temperature. See, for example, U.S. Pat. No. 3,079,228. As is known, bauxite and especially more abundant aluminum-bearing clays contain impurities, particularly iron, and thus, the crude alum liquors produced therefrom contained, in addition to 6 to 11% alumina calculated as Al.sub.2 O.sub.3 metallic impurities (iron) and, insoluble impurities. U.S. Pat. Nos. 3,323,865 and 3,479,136 disclose processes for removing metallic impurities such as iron from crude alum liquor. The insoluble impurities have been separated from the hot liquor which has been then evaporated to remove sufficient water to produce dry aluminum sulfate, Al.sub.2 (SO.sub.4).sub.3.14H.sub.2 O. Due to increased raw material costs, domestic alumina-bearing clays have replaced the more expensive bauxite. In addition, because of increased energy costs, any reduction in evaporative processing cost of alum liquors would be desirable. U.S. Pat. No. 3,141,743, for example discloses a process for the crystallization of aluminum sulfate from a pregnant sulfuric acid solution of the same.
Accordingly, it is an object of this invention to provide a non-evaporative process for the production of pure drier aluminum sulfate, especially pure Al.sub.2 (SO.sub.4).sub.3.14H.sub.2 O